Flora of Thailand Euphorbiaceae

This website page deviates from the Flora of Thailand, as data are mainly replaced by R.Y.Yu & Welzen (2020) and augmented with R.Y.Yu & Welzen (2018, 2019-section classification)

85. Trigonostemon

Goto on this page:

Genus description

Identification key

Species descriptions

Trigonostemon

Blume, Bijdr.: 600. 1826; Fl. Javae: viii. 1828, nom. cons.; Baill., Étude Gén. Euphorb.: 340. 1858; Müll.Arg. in DC., Prodr. 15, 2: 1105. 1866; Benth. in Benth. & Hook., Gen. Pl. 3: 298. 1880; Hook.f., Fl. Brit. Ind. 5: 395. 1887; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii: 85. 1911; Gagnep. in Lecomte, Fl. Indo-Chine 5: 309. 1925; Pax & K.Hoffm. in Engl. & Harms, Nat. Pflanzenfam. ed. 2, 19C: 169. 1931; Backer & Bakh.f., Fl. Java 1: 495. 1963; Airy Shaw, Kew Bull. 20: 47. 1966; Kew Bull. 21: 407. 1968; Kew Bull. 23: 126. 1969; Kew Bull. 25: 545. 1971; Kew Bull. 26: 344. 1972; Whitmore, Tree Fl. Malaya 2: 134. 1973; Airy Shaw, Hooker’s Icon. Pl. 38: t. 3721. 1974; G.L.Webster, Ann. Missouri Bot. Gard. 81: 108. 1994; Philcox in Dassan., Rev. Handb. Fl. Ceylon 11: 110. 1997; Radcl.-Sm., Gen. Euphorbiacearum: 307. 2001; Chantar. in Welzen & Chayam., Fl. Thailand 8, 2: 573. 2007; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11: 171. 2014; R.Y.Yu & Welzen, Blumea 62: 182. 2018; R.Y.Yu et al., Taxon 68: 927. 2019; R.Y.Yu & Welzen, Blumea 65: 25. 2020. — Enchidium Jack, Malayan Misc. 2(7): 89. 1822, nom. rej.; Baill., Étude Gén. Euphorb.: 652: 1858. — Telogyne Baill., Étude Gén. Euphorb.: 652: 1858. — Tylosepalum Kurz ex Teijsm. & Binn., Natuurk. Tijdschr. Ned.-Indië 27: 50. 1864. — Actephilopsis Ridl., Bull. Misc. Inform., Kew 1923: 360. 1923.

Shrubs or small trees, monoecious. Stipules minute, triangular or subulate, caducous. Leaves spiral at the end of the branches, rarely subopposite; usually triplinerved. Inflorescences raceme-like, spikes or panicles, rarely cymes, axillary or terminal, often apparently unisexual. Flowers pedicelled; sepals 5; petals 5, dark purplish red, red, orange-yellow or white, usually drying blackish; disc usually entire and annular or cupular, or consisting of 5 free glands. Staminate flowers with 3 or 5 stamens, filaments united in to a column, but apically free and spreading; pistillode absent. Pistillate flowers with 3-locular ovary; one ovule per locule; style bifid or twice bifid. Fruit a capsule, 3-lobed, smooth, glabrous or pubescent, splitting into 3 bivalved parts, calyx persistent, sometimes enlarged. Seeds globose to 3-gonous-ovoid.

    A genus of 50-60 species, distributed from India and Sri Lanka to China, SE Asia, New Guinea and Queensland. Fourteen species in Thailand. For sectional classification see Yu et al., Taxon 

Key to the species

1. Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl., Handl. Fl. Ned. Ind. 3 (1): 284. 1900; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii: 93. 1911; Airy Shaw, Kew Bull. 28: 126. 1969; Chantar., Thai Forest Bull. (Bot.) 33: 23. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 576. 2007; R.Y.Yu & Welzen, Blumea 62: 187, fig. 1, map 2. 2018; R.Y.Yu et al., Taxon 68: 930. 2019; R.Y.Yu & Welzen, Blumea 65: 28, map 2. 2020. — Tylosepalum aurantiacum Kurz ex Teijsm. & Binn., Natuurk. Tijdschr. Ned.-Indië 27: 50. 1864. — Codiaeum aurantiacum (Kurz ex Teijsm. & Binn.) Müll.Arg. in DC., Prodr. 15, 2: 1118. 1866. — Actephila aurantiaca (Kurz ex Teijsm. & Binn.) Ridl., Bull. Misc. Inform., Kew 1923: 360. 1923; Fl. Malay Penins. 3: 197. 1924. — Actephilopsis malayana Ridl., Bull. Misc. Inform., Kew 1923: 361. 1923; Fl. Malay Penins. 3: 252. 1924; M.R.Hend., J. Malay Br. Roy. As. Soc. 17: 68. 1939. — Trigonostemon malayanus (Ridl.) Airy Shaw, Kew Bull. 20: 413. 1966.  — Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl. var. rubiflorus N.P.Balakr. & Chakrab., J. Econ. Taxon. Bot. 5: 169. 1984.

Shrubs or small trees, 1.5–3(–6) m tall, stem up to 10 cm diam; flowering branches up to 2 mm thick, smooth, brownish. Bark c. 2 mm diam; sap red and sticky; wood pale brown. Stipules subulate, 0.8–1 mm long, hirsute. Leaves: petiole 0.5–3 cm long (depending on leaf size), slightly wrinkled and grooved above, more or less pubescent; blade elliptic to oblong, 8–30 by 2.5–12 cm, chartaceous to coriaceous, base acute, with 2 glands adaxially, occasionally developing into stipellae, margin distantly serrate, teeth falcate or subulate, apex acuminate, young blade reddish, mature ones dark green above, light green beneath, glabrous or scattered pubescent on lower side; venation penninerved, midrib slightly raised above, distinctly elevated beneath, nerves 8–15 pairs, straight, branched and connected near margin, small veins reticulate, often obscure. Inflorescences: staminate ones cauline, few short and condensed thyrses, 6–15 cm long, often bracteolate and with 1 flower per node; pistillate ones terminal or axillary, to 15 cm long, often racemose or paniculate, sometimes mixed with a few staminate flowers; bracteate under each branch and flower, the main rachis (and sometime secondary rachises) often subtended by large, leaf-like bracts, shortly (up to 5 mm) petiolate, blade elliptic or ovate, up to 7 by 3.5 cm, base often cordate, apex acuminate. Staminate flowers c. 6 mm diam; pedicel very slender, up to 1 cm long, c. 0.1 mm diam, pinkish, glabrous; sepals unequal, oblong, 1.2–1.5 by 0.5–1 mm, imbricate, yellowish or reddish, connate at base, apex rounded, more or less pubescent outside, with an often showy gland in the middle outside; petals oblong, c. 4 by 1.3 mm, orange, with a reddish honey mark at base, visible on both sides, inside often paler and outside sometimes with whitish margin, few parallel veins often visible, apex acute, glabrous on both sides; disc glands more or less trapezoid, thick and fleshy, c. 0.2 by 0.5 mm, c. 0.2 mm thick, apex flat; stamens 3, androphore erect, c. 0.5 mm long, trifid at top, anthers free, divaricate, each theca c. 0.6 by 0.2 mm. Pistillate flowers c. 5.5 mm diam, pedicel thickening towards apex, up to 13 mm long, apically c. 0.7 mm diam when flowering, up to c. 2 cm long and apically c. 1 mm diam when fruiting, glabrous; sepals as in staminate flowers, persistent in fruits; petals obovate, 1.5–3.5 by 1–2 mm, orange outside and paler inside, base cuneate or somewhat claw-like, with a reddish (dark reddish pigment granules in epidermis cells visible) honey mark, apex often rounded; disc lobes broad, almost rectangular, truncate at apex, c. 0.3 by 0.7 mm, thin, membranous; ovary c. 1.1 mm diam, glabrous, light yellowish; styles short, 0.2–0.3 mm long, stigmas 3, light yellowish, slightly thickened, apically split and somewhat horseshoe-shaped. Fruits c. 1.2 cm diam, greenish to reddish, glabrous; sepals not accrescent; wall c. 1 mm thick; columella  c. 5.5 mm long. Seeds trigonous, 5.5–9 by 4.4–7 mm, dark orange when dry, hilum somewhat heart-shaped or rhombic, c. 1.5 mm diam.

    Thailand.— PENINSULAR: Surat Thani (Ko Samui), Phuket (Thalang), Satun (Tarutao), Songkhla (Padang Besar, Saba Yoi), Pattani (Khao Kala Khiri), Yala (Banang Sta), Narathiwat (Bachow).

    Distribution.— India (Andaman Is.), Malay Peninsula, Banka (type), Java. Bali

    Ecology.—Lowland evergreen (often dipterocarp) forests, growing in understorey on limestone, along streams or on hill slopes. Altitude: 0–600 m. Flowering and fruiting: all year round.

    Note.—Subgenus Tylosepalum.

2. Trigonostemon capillipes (Hook.f.) Airy Shaw, Kew Bull. 20: 413. 1966; Kew Bull. 26: 145. 1972; Whitmore, Tree Fl. Malaya 2: 134. 1973; Milne, Kew Bull. 50: 45. 1995; Chantar., Thai Forest Bull. (Bot.) 33: 24. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 576. 2007; R.Y.Yu & Welzen, Blumea 62: 191, map 4. 2018; R.Y.Yu et al., Taxon 68: 927. 2019; R.Y.Yu & Welzen, Blumea 65: 29, map 1. 2020. — Dimorphocalyx capillipes Hook.f., Fl. Brit. Ind. 5: 404. 1888; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii: 33. 1911; Ridl., Fl. Malay Penins. 3: 266. 1924.

Shrubs or small trees, 1–8 m tall; flowering branches 1.7–3.2 mm diam. Bark 0.1–0.2 mm thick, brownish to greyish, slightly pubescent near young parts, smooth; wood pale yellowish. Stipules subulate, 0.5–2.3 mm long, caducous, pubescent at base. Leaves: petiole 0.3–1(–2.5) cm long, grooved above, pubescent; blade oblanceolate, oblong or obovate, 9–20 by 3–7 cm, chartaceous, base acute to obtuse, with 2 adaxial glands, margin distantly serrate, teeth small, falcate, apex acuminate, upper side glabrous, lower side paler, slightly pubescent and more or less ciliate along margin; midrib slightly raised on both sides, nerves 9–14 pairs, connected along margin, small veins reticulate. Inflorescences: staminate ones thyrsoid, branched (paniculate), 4–8 cm long, glabrescent, axillary or cauliflorous; bracts leaf-like, elliptic to oblong, up to 10 by 4 mm, slightly pubescent abaxially; pistillate inflorescences cymose, peduncles slender, 1–15 cm long, 0.2–0.5 mm diam, often only one flower at top (sometimes with few depauperate flowers below); bracts as in staminate inflorescences, 4–20 by 1–5 mm. Staminate flowers c. 6 mm diam; pedicel 0.2–1 cm long, 0.1 (middle part)–0.2 (top) mm thick, glabrescent or slightly pubescent; sepals elliptic, c. 1.6 by 1.2 mm, pale green, apex rounded or slightly notched, under the notch often with a gland on outside surface, but sometimes faint or only a few expanded cells; petals elliptic or spathulate, 3–3.5 by 1.5–1.8 mm, base narrowed, acute to cuneate, sometimes claw-like, entire, apex rounded, dark purple, in mature flowers with an orange flame-like honey mark in the middle of the lower part, smooth and glabrous outside, rough and papillose inside; disc lobes almost obtrapezoid, c. 0.35 by 0.3 mm, c. 0.1 mm thick, apex thickened and slightly reflexed, glabrous; stamens 5, androphore c. 0.6 mm long, c. 0.2 mm diam, 5-branched at c. 0.1 mm below apex, filaments c. 0.1 mm long, anthers c. 0.7 mm long, pinkish, divaricate, connectives apically with numerous dark reddish droplets (or expanded cells) with secretion. Pistillate flowers c. 1 cm diam, pedicel slightly thickening towards apex, 6–10 mm long, apically c. 0.7 mm diam when flowering, in fruit accrescent to 1.5 cm long and apically c. 2 mm diam, slightly pubescent; sepals oblong to lanceolate, 2 larger, 4.7–5 by c. 2 mm, 3 smaller, 3.7–3.8 by c. 1.5 mm when flowering, accrescent to 5–15 by 2–6 mm in fruit, pale green, margin slightly serrate, teeth glandular, apex acute to acuminate; petals as staminate flowers but larger, c. 5 by 2 mm; disc lobes rectangular, c. 0.4 by 0.6, apex truncate, corners rounded; ovary c. 1 mm diam, densely hairy, style c. 0.1 mm long, often indistinct, stigmas nearly completely divided, c. 0.9–1 mm long, free arms c. 0.8 mm long, slightly thickened abaxially. Fruits 16–21 by 4–7 mm, finely hairy; sepals and stigmas persistent, stigmas flattened at base, abaxially hairy; wall c. 0.4 mm thick, exocarp not detaching; columella c. 5 mm. Seeds c. 6 mm diam; hilum heart-shaped, 1–1.6 by 1.4–1.5 mm.

    Thailand.— SOUTH-EASTERN: Chanthaburi (Khao Soi Dao; Kerr 19429, type of T. pachyphyllus, holo K); SOUTH-WESTERN: Uthai Thani (Katatak); PENINSULAR: Ranong (Khao Pawta Chong Dong, Khao Pawta Luang Khieo), Nakhon Si Thammarat, Narathiwat (Waeng).

    Distribution.— Malay Peninsula (Singapore type).

    X = T. capillipes; n= T. kerrii

    Ecology.— Lowland rainforest to mangrove forest. Altitude: 0–300 m. Flowering: December to April; fruiting: December to February.

    Note.— Section Trigonostemon.

3. Trigonostemon eberhardtii Gagnep., Bull. Soc. Bot. France 69: 749. 1922; in Lecomte, Fl. Indo-Chine 5: 313. 1925; R.Y.Yu et al., Taxon 68: 931. 2019; R.Y.Yu & Welzen, Blumea 65: 31, fig. 1, map 6. — Trigonostemon harmandii Gagnep., Bull. Soc. Bot. France 69: 750. 1922. — Trigonostemon poilanei Gagnep., Bull. Soc. Bot. France 69: 753. 1922.  — Trigonostemon albiflorus Airy Shaw, Kew Bull. 25: 547. 1971; Chantar., Thai Forest Bull. (Bot.) 33: 23. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 574, fig. 92. 2007. — Trigonostemon leucanthus Airy Shaw, Kew. Bull. 25: 548. 1971.  — Trigonostemon leucanthus Airy Shaw var. siamensis H.S.Kiu in Kiu & Chen, Guihaia 12: 211. 1992. — Trigonostemon wui H.S.Kiu, J. Trop. Subtrop. Bot. 3: 19, f. 2. 1995.

Shrubs or small trees, 1–5(–7) m tall, dbh 2.8–6.3 cm; flowering branches 1.1–5 mm diam, pubescent when young, glabrous in old parts. Indumentum of simple hairs; translucent (oil?) dots often present in green parts (and sometimes petals). Outer bark c. 0.1 mm thick, dark to pale brown or greyish brown; inner bark 0.1–0.2 mm thick, brown to reddish brown; wood white to pale yellowish. Stipules subulate, 0.3–0.7 mm long, caducous, often pubescent. Leaves: petiole terete, grooved or flat above, 0.5–8 cm long, 0.7–2.1 mm diam, glabrous or pubescent; blade elliptic, 8.5–26 by 2.5–8 cm, chartaceous, base acute, 2 adaxial glands present, occasionally sparsely pubescent, margin entire or very distantly serrate, apex acuminate to caudate, upper surface glabrous, dark green, lower surface often very sparsely pubescent, pale green; venation triplinerved, midrib (and sometimes 2 basal secondary veins) slightly raised above and distinctively elevated beneath, pubescent on lower surface, especially near base, other secondary veins 4–7(–10) pairs, bow-shaped and connected along margin, tertiary veins scalariform, veinlets reticulate. Inflorescences bisexual, terminal or axillary, paniculate, pistillate flowers open before staminate ones; main axis terete, up to 31.5 cm long, 0.4–2.7 mm diam, pubescent to glabrous; bracts linear to lanceolate to triangular, 0.7–2.7 by 0.3–0.6 mm, pubescent outside; bracteoles linear to lanceolate, 0.4–0.7 by 0.1–0.2 mm, densely pubescent. Staminate flowers 6–8 mm diam; buds conical; pedicel 2–9.5 mm long, 0.15–0.3 mm diam, glabrous, light green; sepals elliptic, 1–2.3 by 0.5–0.7 mm, light green, base connate, margin entire, apex acute, often with a short notch and an adaxial gland, pubescent outside; petals obovate, 2.8–5 by 1.5–3 mm, contort, membranous, white, lower part cuneately narrowed, apex rounded, glabrous; disc annular, yellow, margin undulate, often deeply notched, 0.4 (inner margin)–0.6 mm (outer margin) diam; stamens 3, androphore 0.9–1.2 mm long, 0.1–0.2 mm diam, white, free part of filaments c. 0.2 mm long, white, anthers free, globose to ellipsoid, 0.3–0.4 mm long, yellow. Pistillate flowers 6–9 mm diam; buds conical; pedicel slightly thickening toward apex, 3–15.5 mm long, apically 0.45–1.1 mm diam when flowering, glabrescent; sepals as staminate flowers but larger, 1.3–3.8 by 0.6–1.3 mm, apex often with an adaxial gland but without notch; petals as staminate flowers; disc lobes 5, rectangular, 0.3–0.45 by 0.3–0.4 mm, yellow, apex truncate; ovary 1–1.1 mm diam, glabrous, green, style 0.1–0.2 mm long, stigmas 0.8–1.1 mm long, bent, white, apically slightly thickened and slightly bifid. Fruits 1.1–1.5 cm diam, greenish, glabrous; pedicel 1.9–3.4 cm long, 1.2–1.8 mm diam; sepals persistent but not accrescent; wall 0.4–0.5 mm thick, exocarp partly detaching; columella 4.5–6.5 mm long. Seeds 7–8 mm diam, marbled; hilum rhombic, 2.5–3 by 1–2 mm.

    Thailand.— NORTHERN: Chiang Mai (Doi Chiangdao), Nan, Lampang (Wang Nua, WINIT 1704-holotype K, isotypes BKF, BM); SOUTH-EASTERN: Chanthaburi (Soi Dao).

    Distribution.— China (Kwangsi), Thailand, Laos, Cambodia, Vietnam.

    « = T. eberhardtii; X = T. quocensis

    Ecology.— Evergreen or deciduous forests, growing on limestone, sometimes in shaded areas near rivers. Elevation: 150–1300 m. Flowering: March to December; fruiting: May to December. 

    Notes.— 1. Trigonostemon eberhardtii is characterised by the translucent (oil?) dots and white petals (the label of a specimen from Thailand, Sangkhachand 531, indicates that the petals are yellow, but this is a very exceptional case and the label could be wrong). Although the dots are not always present in all green parts (young branches, petiole, leaf blade, inflorescences, sepals, ovary and fruits), when present, it is a good spotting character, particularly in herbarium material. 

2. The species resembles T. viridissimus, with which the morphological boundary is sometimes unclear. However, the molecular phylogeny (Yu et al. 2019) shows that the two species are placed in different subclades within sect. Tylosepalum. Main characters that can be used in identification include: 1) the white petals (yellow to orange in T. viridissimus); 2) monopodial branching in the inflorescences with relatively more condensed staminate flowers (vs sympodial branching and relatively loose panicles in T. viridissimus var. viridissimus); and 3) an indistinctive style (shorter than 2 mm in T. eberhardtii; up to 6 mm in T. viridissimus).

4. Trigonostemon flavidus Gagnep., Bull. Soc. Bot. France 69: 74. 1922; in Lecomte, Fl. Indo-Chine 5: 320. 1925; P.T.Li & M.G.Gilbert in C.Y.Wu, P.H.Raven & D.Y.Hong, Fl. China 11: 273. 2008; R.Y.Yu & Welzen, Blumea 62: 194, map 4. 2018; R.Y.Yu et al., Taxon 68: 927. 2019; R.Y.Yu & Welzen, Blumea 65: 33, fig. 2, map 7. 2020. — Trigonostemon heterophyllus Merr., Lingnan. Sc. Journ. 9: 38. 1930; H.S.Kiu, Fl. Reipubl. Popul. Sin. 44(2): 163. 1996; Chantar., Thai Forest Bull. (Bot.) 33: 24. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 577, Plate XXXI: 1. 2007. — Trigonostemon sunirmalii Chakrab. & N.P.Balakr., J. Econ. Taxon. BOt. 5: 179. 1984.

Small trees, 1–2.5 m tall; flowering branches up to 4.5 mm diam, densely pubescent. Outer bark 0.1–0.2 mm thick, pale brown to dark grey, smooth or roughened; inner bark 0.1–0.2 mm thick, reddish brown; wood pale yellow. Stipules subulate, 0.7–1 mm long, pubescent at base. Leaves: petiole terete but sometimes flattened or grooved above, 0.2–1.2 cm long, 0.7–2.4 mm diam, densely pubescent; blade obovate or oblanceolate, cuneately narrowed and sometimes unequal in the lower middle part, 9–35 by 5–9 cm, chartaceous, base abruptly rounded to truncate, with 2 adaxial glands, margin distantly serrate, teeth small and nipple-like, apex caudate to acuminate, upper surface dark to light green, lower surface paler, both surfaces pubescent, especially on secondary veins and margin; venation pinnate; midrib thin, elevated on both surfaces, secondary veins 10–13 pairs, tertiary veins reticulate, often obscure. Inflorescences bisexual, in short cymes or thyrses, cauliflorous or supported by a peduncle and involucral bracts; peduncle 1–9 cm long, pubescent; involucral bracts lanceolate, 8–38 by 0.7–9 mm, pubescent; bracts lanceolate to linear, 1.1–5.5(–15) by 0.2–0.7(–2) mm, pubescent. Staminate flowers 3.6–6 mm diam; pedicel 2.4–4.7 mm long, 0.15–0.3 mm thick, pink to light green, glabrous; sepals elliptic or obovate, 1.1–2.4 by 0.5–1.8 mm, green, base connate, margin ciliate, apex often acute to rounded, occasionally with a notch, pubescent outside; petals obovate, 2.1–4.2 by 1.7–2.2 mm, base claw-like, apex rounded, glabrous, dark reddish to maroon-purple to black; disc lobes obovate or rectangular, 0.4–0.7 by 0.15–0.25 mm, sometimes narrowed at base, often reflected at apex, light orange, glabrous; stamens 3, androphore 1–1.2 mm long, c. 0.1 mm diam, white, shortly trifid at apex, free part of filaments 0.1–0.2 mm long; anthers free, divaricate at apex, thecae 0.4–0.6 mm long, pale yellow, connective pinkish red, with numerous droplets with secretion. Pistillate flowers few, slightly enlarged when fruiting, up to c. 1 cm diam; pedicel c. 1.5 mm long and c. 0.5 mm diam in flower bud, accrescent to c. 7 mm long and apically c. 1 mm diam when fruiting; sepals lanceolate to linear, 2.2–3.4 by 1–1.5 mm when flowering, accrescent to 2.4 by 0.9 cm in fruit, margin entire or with a few teeth, apex acuminate, pubescent outside; petals elliptic, 3–3.3 by 2–2.7 mm (flower bud), caducous; disc glands rectangular to semi-orbicular, 0.5–0.6 by 0.4–0.6 mm, rounded or truncate at apex, glabrous; ovary c. 0.7 mm diam, bright dark green, densely pubescent, style almost indistinct, stigmas 3, completely divided, free arms 0.6–0.7 mm long. Fruits c. 1.2 cm diam, green when young, brown when mature, densely pubescent; wall woody, 0.5–0.55 mm thick; columella 4.2–6.7 mm long. Seeds 4.2–6.7 by 4.5–5.7 mm, light or dark brownish when dry, hilum irregularly shaped, more or less triangular, 0.8–1.3 by 0.5–0.7 mm diam.

    Thailand.— NORTH-EASTERN: Nong Khai (Phu Wua).

    Distribution.— Myanmar (Tenasserim), China (type), Laos, Thailand, Malay Peninsula.

    Ecology.— Understorey in evergreen forests to deciduous hardwood or bamboo forests, often near rivers, growing on sandstones to conglomerate bedrocks. Elevation: 200–400 m. Flowering: January to March, July; fruiting: February, July to October.

    Note.— Section Trigonostemon.

5. Trigonostemon kerrii Craib, Bull. Misc. Inform., Kew 1924: 97. 1924; Gagnep. in Lecomte, Fl. Indo-Chine 5: 321. 1925; Chantar., Thai Forest Bull. (Bot.) 33: 25. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 577. 2007; R.Y.Yu et al., Taxon 68: 928. 2019; R.Y.Yu & Welzen, Blumea 65: 36, map 1. 2020.

Shrubs or small trees, 2–3 m tall; flowering branches 1.5–2.8 mm diam, pubescent when young, glabrous in old parts. Outer bark 0.1–0.2 mm thick, pale grey to brown; inner bark c. 0.1 mm thick, dark reddish; wood pale yellowish to white. Stipules subulate, 0.5–1 mm long, caducous, pubescent at base. Leaves: petiole terete but grooved above, 0.7–2.8 cm long, 0.9–1.2 mm diam, slightly pubescent; blade oblong to oblanceolate, 10.5–21 by 1.8–4.4 cm, chartaceous, base acute, with 1–2 pairs of adaxial glands, margin distantly serrate, teeth glandular, apex acuminate, upper surface glabrous, lower surface glabrescent; venation pinnate, midrib slightly raised above and elevated beneath, slightly pubescent beneath, secondary veins 8–11(–16) pairs, curved and connected along margin, tertiary veins reticulate, often obscure. Inflorescences seemingly unisexual, subterminal; staminate ones racemose thyrses, pistillate ones racemes; axis 1–11.2 cm long, 0.4–0.75 mm diam, pubescent; bracts lanceolate, 0.5–3.6 by 0.2–0.9 mm, pubescent. Staminate flowers c. 2.8 mm diam; pedicel 2.5–6 mm long, 0.1–0.2 mm diam, glabrescent; sepals elliptic to lanceolate, 0.9–1.5 by 0.5–0.9 mm, base connate, margin often serrate, apex acuminate to rounded, pubescent outside; petals in flower bud elliptic, 1.1–1.4 by 0.7–0.9 mm, apex rounded, purplish red (Craib 1924); disc glands 5, c. 0.15 by 0.1 mm; stamens 3, androphore indistinct (flower too young), anthers ellipsoid, 0.7–0.8 mm long. Pistillate flowers (bud) c. 1.7 mm diam; pedicel c. 2.6 mm long, 0.4–0.5 mm diam, glabrescent; sepals triangular, 1.6 –1.9 by 0.7– 0.9 mm, base connate, margin fringed with capitate glands, apex acuminate; petals elliptic, 1.7–2.2 by 1–1.3 mm, apex rounded, purplish red (Craib 1924); disc glands 5, c. 0.2 by 0.2 mm; ovary c. 0.7 mm diam, glabrous, style absent, stigmas c. 0.25 mm long, apically seemingly bifid. Fruits glabrous; pedicel c. 1.8 cm long, c. 0.7 mm diam, glabrescent; sepals accrescent, persistent, lanceolate, 5–6 by 1.5–2 mm, margin fringed with capitate glands; wall 0.3–0.4 mm thick, exocarp not detaching; columella c. 3 mm long. Seeds not seen.

    Thailand.— NORTHERN: Tak, Phitsanulok (Nakhon Thai-KERR 5871, lectotype BK, isolectotypes BM, K, TCD).

    Distribution.— hailand, Cambodia (Kampong Thom). 

    X = T. capillipes; n= T. kerrii

    Ecology.— In evergreen forests. Elevation: 100– 200 m. Flowering: March; fruiting: April.

    Note.— Section Trigonostemon.

6. Trigonostemon laevigatus Müll.Arg., Flora 47: 538. 1864; in DC., Prodr. 15, 2: 1111. 1866; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii: 94. 1911; Ridl., Fl. Malay Penins. 3: 265. 1924; Jablonski, Brittonia 15: 167. 1963; Chantar., Thai Forest Bull. (Bot.) 33: 25. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 578, Fig. 93. 2007; R.Y.Yu & Welzen, Blumea 62: 195, fig 5, map 5. 2018; R.Y.Yu et al., Taxon 68: 930. 2019; R.Y.Yu & Welzen, Blumea 65: 36. 2020. — Trigonostemon anomalus Merr., Philipp. J. Sci. 16: 569. 1920; Enum. Philip. 2: 451. 1923. — Trigonostemon petelotii Merr., Univ. Calif. Publ. Bot. 10: 425. 1924. — Trigonostemon laevigatus Müll.Arg. var. petiolaris Airy Shaw, Kew Bull. 32: 417. 1978.

Trees, 5–15 m tall, stem up to 15 cm diam; flowering branches 1.5–2 mm diam, often slightly pubescent near nodes and apical buds. Bark 0.3–0.5 mm thick, smooth, lenticellate, light greenish to pale or dark brownish to blackish; sap red, pink or colourless; wood whitish to reddish brown, with brownish pink rays. Stipules falcate to nipple-like, 0.3–1 mm long, pubescent, caducous, often obscure or not seen. Leaves: petiole terete but often flat or grooved above, 0.5–1.5(–4) cm long, wrinkled, glabrescent to pubescent, base and apex sometimes pulvinate; blade elliptic, sometimes oblong, ovate or oblanceolate, 6–20 by 2.5–8 cm, chartaceous or coriaceous, base acute to cuneate, with 2 adaxial glands, margin entire, apex acuminate to caudate, above greenish, underneath pale green below, both sides glabrous; venation triplinerved, midrib elevated beneath, nerves 6–9 pairs, bow-shaped, narrowed along margin, veinlets reticulate, obscure. Inflorescences terminal or axillary, cymes or paniculate thyrses, abbreviated and condensed or elongated and lax, 0.5–4 cm long, often branched, glabrescent or pubescent, bracts long-triangular to linear, up to 3 by 1 mm, velutinous. Staminate flowers 6–10 mm diam; pedicel c. 1 cm long, c. 0.2 mm thick, scarcely pubescent; sepals oblong to obovate to orbicular, 2–4.5 by 1.8–2.5 mm, sometimes unequal, then outer 2 or 3 larger, imbricate, margin entire, apex rounded, yellowish green, often finely puberulent on both sides, outside also pubescent with longer hairs and sometimes with a subapical gland (var. croceus); petals flabellate and bilobed, each lobe 3–6 by 1.5–3 mm, yellow or reddish, glabrous, few parallel veins visible, base claw-like, apex notched to 1/3 to 1/2 of length and often with a small gland below the notch; disc annular, c. 0.5 mm high, glabrous, apex recurved; stamens 3, androphore 0.3–1.5 mm high, trifid at apex, filaments 0.2–0.5 mm long, anthers oblong, c. 0.8 mm long, yellow, free, base somewhat auriculate, not divaricate at apex. Pistillate flowers c. 6 mm diam, pedicel thickened towards apex, up to 2.5 cm long, apically c. 1 mm thick, slightly pubescent; sepals, petals and disc as in staminate flowers; ovary c. 1 mm diam, greenish, glabrescent to densely hairy, style c. 0.1 mm long, sometimes indistinct, stigmas 3 separate arms, c. 0.6 mm long, c. 0.1 mm thick, apex very slightly thickened and bifid. Fruits c. 1 cm diam, greenish, finely hairy; wall 0.4–0.6 mm thick, exocarp detaching; columella 5–6.5 mm long. Seeds 7–8 by 6–7 mm; hilum 1.5–3 by 1–2 mm.

    Thailand.— PENINSULAR: Ranong (Khao Pawta Luang Khieo), Nakhon Si Thammarat (Khiriwong), Satun (Tarutao), Narathiwat (Sungei Kolok).

    Distribution.— Myanmar, Indo-China, Malay Peninsula, Borneo (Kalimantan-type), Philippines.

    Ecology.— In evergreen forest. Altitude: 50-1,300 m.

    Note.— Section Tylosepalum.

Key to the varieties

a. var. laevigatus: R.Y.Yu & Welzen, Blumea 62: 197, fig. 5, map 5: 2018; Blumea 65: 36, map 9. 2020..

 

 

Sepals without a gland outside.

    Distribution.— Vietnam?, Thailand, Malay Peninsula, Sumatra, Java, Borneo, Philippines.

    l = T. laevigatus var. laevigatus; «= T. laevigatus var. croceus

    Ecology.— Mixed lowland dipterocarp forest, growing on clay to sandy soils to basalt derived soils of hill slopes. Altitude: 30–600 m. Flowering: all year round; fruiting: April, August, September, November.

    Notes.— 1. The variety generally has a short petiole (often shorter than 1.5 cm) but it can be up to 4 cm long in some populations (e.g., in some populations from Brunei and Sabah). Since the variance is continuous, Airy Shaw’s var. petiolaris is synonymised here.

    2. The sepals often have 2 layers of hairs on the outside, the relatively stiffer and longer hairs form the upper layer and often a layer of very dense and fine hairs that forms the lower layer and which is also present on the inside.

 

b. var. croceus (B.C.Stone) R.Y.Yu & Welzen, Blumea 62: 197, map 5. 2018; Blumea 65: 37, map 9. 2020.  —  Trigonostemon croceus B.C.Stone, Malaysian Forester 43: 289. 1980.

 

Sepals with a gland outside.

    Distribution.— Thailand, Malay Peninsula.

    l = T. laevigatus var. laevigatus; «= T. laevigatus var. croceus

    Ecology.— Hill evergreen forest to grassy sites. Altitude: 900–1300 m. Flowering: November to May.

    Note.— Stone (1980) newly described T. croceus, because it had 5 instead of the 3 stamens of T. laevigatus. We dissected one staminate flower from the isotype and it turned out to have 3 stamens. Its only difference from the typical T. laevigatus are the showy, protruding glands on the sepals, but there is a continuous variation from being glandless to having a flat gland to even having a protruding gland. However, according to the specimen notes the croceus form occurs at higher altitudes than the typical laevigatus form. Therefore, T. croceus is here regarded as a variety of T. laevigatus.

7. Trigonostemon lanceolatus (S.Moore) Pax in Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii: 92. 1911; R.Y.Yu et al., Taxon 68: 928. 2019; R.Y.Yu & Welzen, Blumea 65: 37, map 3. 2020. — Nepenthandra lanceolata S.Moore, J. Bot.: 149, pl. 471, f. 7–13. 1905. — Trigonostemon phyllocalyx Gagnep., Bull. Soc. Bot. France 69: 753. 1923; in Lecomte, Fl. Indo-Chine 5: 312. 1925; P.H.HÔ, Câyco Viêtnam 2(1): 341. 1992; Chantar., Thai Forest Bull. (Bot.) 33: 27. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 581. 2007.

Trees, up to 5 m tall, dbh up to 5 cm; flowering branches 1.9–3.5 mm diam, pubescent when young, glabrous in old parts. Outer bark 0.1–0.2 mm thick, brown to pale or greyish brown; inner bark 0.1–0.2 mm thick, reddish brown, sap red; wood yellow to brown. Stipules subulate, 0.4–1.1 mm long, caducous, pubescent at base. Leaves: petiole terete, grooved above, 1.4–11.5 cm long, 0.8–2 mm diam, hirsute to glabrous; blade lanceolate to oblong, 6.8–21 by 2.3–8.2 cm, thick-chartaceous, base acute to rounded, 2 adaxial glands present, margin distantly serrate, apex acuminate to slightly caudate, both surfaces glabrous; venation pinnate, midrib flat or slightly raised above and elevated beneath, sometimes slightly pubescent beneath, secondary veins 6–10 pairs, curved, connected along margin, tertiary veins and veinlets reticulate. Inflorescences bisexual, often axillary, racemose thyrses, pistillate flowers open first, single per node near apex of axis, staminate flowers usually 1–3 per node below; axis up to 8.7 cm long, 0.5–0.8 mm diam, hirsute to glabrescent, bracts oblong, 0.4–6.5 by 0.1–1.4 mm, pubescent. Staminate flowers (bud) c. 2.4 mm diam; pedicel thickening toward apex, 1.8–2.5 mm long, apically 0.4–0.8 mm diam, slightly hirsute; sepals ovate to elliptic, 1.2–1.9 by 0.8–1.5 mm, base connate, margin entire, sometimes ciliate, apex rounded to acute, pubescent or hirsute outside; petals ovate to elliptic, 1.1–1.4 by 0.9–1.15 mm diam, glabrous, apex rounded; disc annular, c. 0.1 mm wide, ring c. 0.8 mm diam; stamens 3, androphore c. 0.1 mm long, anthers ellipsoid, 0.5–0.7 mm long, divaricate. Pistillate flowers 5–10 mm diam; pedicel thickening toward apex, 3–7 mm long, apically 1–1.2 mm diam, pubescent or hirsute; sepals triangular, 4–5.5 by 2.7–3 mm when flowering, significantly accrescent, up to 1.3 by 1.1 cm when fruiting, densely hirsute on both sides, base connate, margin mostly entire but with two teeth near apex, apex acuminate; petals elliptic, 2.5–3 by 1.8–2.6 mm, apex rounded; disc seemingly annular, c. 0.6 mm wide; ovary c. 1.7 mm diam, glabrous to hirsute; style absent; stigmas deeply bifid, 0.6–0.7 mm long, free arms V-shaped at base. Fruits 1–1.1 cm diam, densely hirsute, smooth; sepals persistent; wall 0.3–0.4 mm thick. Seeds c. 7.5 mm diam, marbled; hilum triangular, c. 2.5 by 1.7 mm.

    Thailand.— SOUTH-EASTERN: Chanthaburi (Khao Sabap, Pliew waterfall).

    Distribution.— Myanmar (Tenasserim), Thailand, Vietnam (Annam-type).

    ▲= T. lanceoatus; «= T. pachyphyllus

    Ecology.— Evergreen forests, on rocky or sandy soil, near stream. Altitude: c. 200 m. Flowering: December to March; fruiting: December to January.

    Notes.— Section Trigonostemon.

2. The species is characterised by the much accrescent and hirsute sepals in the pistillate flowers.

8. Trigonostemon longifolius Baill., Étude Gén. Euphorb.: 341.1858 ('longifolium'); Müll.Arg. in DC., Prodr. 15, 2: 1108. 1866; Hook.f., Fl. Brit. Ind. 5: 396. 1887; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii: 88, f. 28. 1911; Ridl., Fl. Malay Penins. 3: 264. 1924; Jablonski, Brittonia 15: 162. 1963; P.H.HÔ, Câyco Viêtnam 2(1): 341. 1992; Chantar., Thai Forest Bull. (Bot.) 33: 26. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 579, Fig. 94. 2007; R.Y.Yu & Welzen, Blumea 62: 197, fig. 6, map 6. 2018; R.Y.Yu et al., Taxon 68: 929. 2019; R.Y.Yu & Welzen, Blumea 65: 37, map 10. 2020. — ?Athroisma dentatum Griff., Notul. 4: 478. 1854 (‘dentatis’).  — ?Athroisma serratum Griff., Notul. 4: 477. 1854 (‘serratis’). — Croton longipedunculatus Elmer, Leafl. Philipp. Bot. 1: 311. 1908. — Trigonostemon longipedunculatus (Elmer) Elmer, Leafl. Philipp. Bot. 4: 1306. 1911. — Trigonostemon oblanceolatus C.B.Rob., Philipp. J. Sci. 6, Bot.: 337. 1911. — Prosartema gaudichaudii Gagnep., Bull. Soc. Bot. France 72: 468. 1925. — Trigonostemon ridleyi Jabl., Brittonia 15: 165, fig. 8. 1963. — Trigonostemon elmeri Merr., Pl. Elmer. Born.: 162. 1929. — Trigonostemon howii Merr. & Chun, Sunyatsenia 2: 262. 1935. — Trigonostemon gagnepainianus Airy Shaw, Kew Bull. 32: 415. 1978. — Trigonostemon matangensis R.I.Milne, Kew Bull. 49: 445, fig. 1. 1994. — Trigonostemon longipedunculatus (Elmer) Elmer var. mollis R.I.Milne, Kew Bull. 50: 27, in key, 29, in key, 40. 1995. — Trigonostemon honbaensis Tagane & Yahara in Tagane et al., Acta Phytotax. Geobot. 68: 39. 2017.

Small trees, 1–5 m tall, stem up to 7 cm diam; flowering branches 2–5(–7) cm diam. Outer bark 0.1–0.25 mm thick, smooth, pubescent to hispid when young, whitish to brownish; inner bark 0.2–0.4 mm thick, yellowish to reddish brown, soft; sapwood 0.8–1.5 mm thick, white to dark brownish; heartwood 2–3 mm diam. Stipules linear to hook-like, 2–8.5 by 0.3–1 mm, often pubescent. Leaves: petiole terete, 0.4–3.5 cm long, often wrinkled, hispid; blade oblanceolate, (10–)12–28(–46) by (2.8–)4–10(–15) cm, membranous to chartaceous to coriaceous, base cuneate to round, margin distantly serrate, apex acuminate to slightly caudate, upper side glabrous to slightly pubescent, lower side often pubescent to hispid; midrib robust, elevated on both sides, nerves (9–)11–16(–33) pairs, often slightly curved and connected along margin, veins scalariform, veinlets reticulate. Inflorescences uni- or bisexual, axillary or terminal, loose or condensed, per node a single flower or short cymes, rachis (7–)15–30(–55) cm long, 0.5–4 mm diam, pubescent; bracts lanceolate to linear, 3–8 by 0.3–1 mm, pubescent. Staminate flowers 4–5 mm diam; pedicel 1.5 (Thailand, Malay Peninsula, Sumatra)–5 (Borneo) mm long, 0.1–0.2 mm diam, pubescent, base articulate; sepals elliptic, 1.2–2 by 0.7–1 mm, green, margin entire, apex rounded, pubescent outside, glabrous inside; petals spathulate to obovate, 2–2.5 by 1.2–1.7 mm, pinkish to bluish black, base slightly claw-like, sometimes with 2 gland lobes (Thailand, Malay Peninsula, Sumatra), margin entire, apex rounded, smooth outside, often rough and papillose inside; disc annular, 0.2–0.4 mm wide, margin often 5-notched; stamens 3, androphore c. 0.4 mm long, trifid at top, anthers free, divaricate, connective sometimes protruding at top (Thailand, Malay Peninsula, Sumatra). Pistillate flowers 4–5 mm diam; pedicel slightly thickened towards apex, 1.7–3 (Thailand, Malay Peninsula, Sumatra)–9 (Borneo) mm long, apically 0.5–1 mm diam; sepals elliptic to lanceolate, 1.2–1.8 by 0.8–1.5 mm, margin entire, apex rounded to acute, pubescent outside, glabrous inside; petals and disc as staminate flowers; ovary c. 0.7 mm diam, densely pubescent, glabrescent, slightly (Thailand, Malay Peninsula, Sumatra, Borneo, Philippines) to extremely (Borneo) warty; styles short, often indistinct, trifid; stigmas bifid into 2 flattened lobes. Fruits 1.2–1.4 cm diam, green, pubescent, glabrescent, slightly to extremely warty; sepals persistent, not accrescent; wall 0.4–0.6 mm thick, exocarp partly splitting off; columella 5.5–6 mm long. Seeds 6.5–7 by 6–6.5 mm; hilum elliptic to rhombic to heart-shaped, 2–4.5 by 2.5–4 mm.

    Thailand.— SOUTH-EASTERN: Chanthaburi; PENINSULAR: Ranong (Khao Pawta Chong Dong, Klong Naka), Krabi (Nong Chik), Nakhon Si Thammarat (Khao Luang, Tasala), Phuket, Phatthalung (See Bahn Pote), Satun (Knan Kalong, Kuan Po), Pattani, Yala (Banang Sta), Narathiwat (Waeng).

    Distribution.— Myanmar (Tenasserim), China, Thailand, Laos, Vietnam, Malay Peninsula (type), Sumatra, Borneo, the Philippines.

    Ecology.— Primary evergreen to logged forests, flat land to hill sides, sometimes near rivers, growing on black soil or sandy or stoney clay. Altitude: 15–1600 m. Flowering and fruiting: all year round.

    Vernacular.— Thao yaai mom paa (เท้ายายม่อมป่า), Aaibaao (อ้ายบ่าว) (Pattani).

    Note.— Section Spinipollen.

9. Trigonostemon malaccanus Müll.Arg., Flora 47 (1864) 482; in A.DC., Prodr. 15, 2 (1866) 1110; Hook.f., Fl. Brit. India 5 (1887) 396; Pax & K.Hoffm. in Engl., Pflanzenfam. IV.147.iii (1911) 90; Ridl., Fl. Malay Penins. 3 (1924) 265; Jabl., Brittonia 15 (1963) 154; Whitmore, Fl. Malay Penins. 2 (1973) 136; Airy Shaw, Kew Bull. 36 (1981) 355; R.Y.Yu & Welzen, Blumea 62 (2018) 201, fig. 8, map 7; R.Y.Yu et al., Taxon 68 (2019) 928; R.Y.Yu & Welzen, Blumea 65 (2020) 38, map 11; R.Y.Yu et al., Taxon 68: 928. 2019; R.Y.Yu & Welzen, Blumea 65: 38, map 11. 2020. — Trigonostemon laetus Baill. ex Müll.Arg. in A.DC., Prodr. 15, 2 (1866) 1109.

Small trees, up to 6 m tall, stem at least up to 5 cm diam; flowering branches up to 7.5 mm thick, glabrous or slightly pubescent in young parts, sometimes hollow. Bark c. 0.3 mm thick, smooth, brownish to greyish to blackish; sap clear or orange; wood pale yellowish. Stipules falcate or subulate, c. 1 mm long, often pubescent near base. Leaves clustered near apex of branches; petiole terete but grooved above, 2.5–22 cm long, sometimes thickened at apex or base, slightly pubescent, glabrescent; blade lanceolate, oblong or occasionally ovate, 10–25(–40) by 3–14 cm, chartaceous to coriaceous, base acute to rounded, with 2 adaxial, subulate or falcate glands, margin distantly serrate, teeth small, falcate or nipple-like, apex acuminate to caudate, glabrous above, sparsely pubescent along venation beneath; midrib elevated and slightly pubescent (glabrescent in large leaves) on lower side, nerves 8–13 pairs, slightly curved and narrowed along margin, veinlets reticulate, often obscure. Inflorescences mainly unisexual, staminate ones thyrsoid, often terminal or subterminal, with short cymes along the main rachis, up to 25 cm long, densely hirsutellous, condensed when young; involucral bracts 2 or more, lanceolate to falcate, up to 2 by c. 0.5 mm; bracteate under cymes and under each flower, bracts lanceolate, up to 2 by 0.9 mm and 0.6 by 0.4 mm, respectively, hirsutulous; pistillate inflorescences racemose or thyrsoid, 1- or few-flowered cyme at each node, sometimes mixed with a few staminate flowers, up to 30 cm long, hirsutulous, condensed when young. Staminate flowers c. 4 mm diam; pedicel 1.5–2 mm long, 3–5 mm diam, hirsutulous; sepals orbicular to obovate, 1–2.1 by 0.6–1.6 mm, apex rounded, puberulent outside and often with a gland in the middle (on young flowers); petals obovate, c. 2.5 by 1.7 mm, pinkish or reddish purple, base cuneate, margin often wrinkled, apex rounded, glabrous on both sides; disc 0.6–1 mm diam, lobes obtrapezoid, c. 0.5 by 0.5 mm, c. 0.1 mm thick, glabrous, fused when young, separate and wrinkled when flowering, apex recurved and flat; stamens 3, androphore erect, c. 0.5 mm high, c. 0.2 mm diam, anthers free, long ellipsoid, c. 0.5 mm long. Pistillate flowers c. 4.5 mm diam; pedicel 1.5–2 mm long, 0.5–0.7 mm diam when flowering, slightly elongating to c. 4 mm long and 1 mm thick in fruit, hirsutulous; sepals and petals as staminate flowers, but petals caducous when fruiting; disc annular, margin irregularly undulate or with notches; ovary c. 1 mm diam, densely pubescent, style absent, stigmas deeply cleft for at least 3/4. Fruits c. 8 mm diam, puberulent, sepals persistent but not accrescent; wall 0.5–0.6 mm thick, exocarp detaching; columella 4.5–6 mm long. Seeds 5.5–6 by 5–5.5 mm; hilum triangular or heart-shaped, 2.5–3 by 2–2.5 mm.

    Distribution.— Thailand, Malay Peninsula, Sumatra.

    Ecology.— Evergreen forests to recently logged-over forests on hill ridges or in valleys, sometimes near rivers. Altitude: 100–850 m. Flowering: all year round; fruiting: June to August, November to February.

    Note.— Section Trigonostemon.

10. Trigonostemon murtonii Craib, Bull. Misc. Inform., Kew 1911: 464. 1911 (‘murtoni’); Pax & K.Hoffm. in Engler., Pflanzenr. IV.147.vi: 128. 1912; P.H.HÔ, Câyco Viêtnam 2(1): 342. 1992; Chantar., Thai Forest Bull. (Bot.) 33: 26. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 581. 2007; R.Y.Yu et al., Taxon 68: 928. 2019; R.Y.Yu & Welzen, Blumea 65: 40, map 8. 2020. — Trigonostemon pierrei Gagnep., Bull. Soc. Bot. France 64: 752. 1923. — Trigonostemon pinnatus Gagnep., Bull. Soc. Bot. France 64: 752. 1923; in Lecomte, Fl. Indo-Chine 5: 318. 1925.

Shrubs, 1–5 m tall; flowering branches 1.1–3.5 mm diam, pubescent when young, glabrous in old parts. Outer bark c. 0.1 mm thick, dark brown to pale grey; inner bark c. 0.1 mm thick, reddish brown; wood pale yellowish. Stipules subulate, 0.3–0.7 mm long, caducous, often pubescent at base. Leaves: petiole terete, grooved above, 0.2–1.9 cm long, 0.7–1.5 mm diam, pubescent; blade oblanceolate to oblong, 5–20 by 1.2–4.3 cm, chartaceous to coriaceous, base rounded to acute, 2 adaxial glands present, margin entire, occasionally with glandular or subulate teeth, apex acuminate to short-caudate, both surfaces glabrous; venation pinnate, midrib elevated on both sides, sometimes furrowed above, often sparsely pubescent beneath, secondary veins 9–18 pairs, curved, bifurcate and connected along margin, tertiary veins reticulate, obscure. Inflorescences bisexual, terminal or axillary racemes (flowers clustered at apex) or panicles (spreading like a broom at apex); peduncle up to 7 cm long, 0.3–0.7 mm diam, pubescent; bracts oblong to lanceolate, 1–8.5 by 0.2–1.5 mm, pubescent on both sides. Staminate flowers 3–5 mm diam; pedicel 3–4.5 mm long, 0.1–0.2 mm diam, pubescent; sepals elliptic, 0.8–1.5 by 0.5–0.8 mm, base connate, margin entire, apex acuminate, acute, rounded or bilobed, pubescent outside; petals obovate to spathulate, 1.6–2.7 by 1–2 mm diam, dark pink, glabrous, apex rounded; disc glands 5, 0.3–0.35 by 0.1–0.15 mm; stamens 3, androphore c. 0.5 mm long, c. 0.25 mm diam, anthers ellipsoid, 0.4–0.5 mm long, connective with droplets (expanded cells) with secretion. Pistillate flowers 3.3–8 mm diam; pedicel thickening toward apex, 3.5–7 mm long, apically 0.5–1 mm diam, elongating to c. 1 cm long in fruit, pubescent; sepals lanceolate, 5–6 by 1–1.6 mm, slightly accrescent to c. 8 by 2.2 mm when fruiting, pubescent outside, especially along midrib, base connate, margin entire, apex acuminate; petals as in staminate flowers; disc lobes rectangular, 0.2–0.25 by 0.25–0.3 mm, apex truncate; ovary 0.6–1.3 mm diam, densely pubescent; style indistinct, less than 0.1 mm long; stigmas apically deeply bifid, free arms coiled. Fruits (young) pubescent. Seeds not seen.

    Thailand.— SOUTH-EASTERN: Trat (Klong Yai, Ko Klone, MURTON 18 - holotype K).

    Distribution.— Thailand, Cambodia, Vietnam (Cochinchina).

    Ecology.— Evergreen forests, on sandy clay and in shaded, rocky areas. Elevation: c. 250 m. Flowering: February, April, June, November; fruiting: April.

    Note.— Section Trigonostemon.

11. Trigonostemon pachyphyllus Airy Shaw, Kew Bull. 25: 546. 1971; Chantar., Thai Forest Bull. (Bot.) 33: 27. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 581. 2007; R.Y.Yu & Welzen, Blumea 65: 40, map 3. 2020.

Shrubs, c. 1.5 m tall; flowering branches 3.2–4 mm diam, glabrescent. Outer bark c. 0.1 mm thick, brown; inner bark 0.1–0.2 mm thick, reddish brown; wood yellow. Stipules subulate, 0.6– 0.8 mm long, caducous, pubescent. Leaves: petiole wrinkled, flat or slightly grooved above, 0.3–1 cm long, 2–2.2 mm diam, pubescent to glabrous; blade oblong, 12–19 by 2.1–3.9 cm, coriaceous, base acute, adaxial glands not seen, margin entire, occasionally with very sparse glandular teeth, apex acuminate, upper surface glabrous, dull green or puplish brown when dry, lower surface sparsely pubescent, yellow when dry; venation pinnate, midrib flat above and elevated beneath, often pubescent beneath, secondary veins 12–15 pairs, curved, bifurcate and connected along margin, tertiary veins reticulate. Inflorescences seemingly unisexual; staminate ones axillary, thyrses, axis 1–1.4 cm long, 0.8–1.1 mm diam, pubescent, bracts triangular, 0.15–1.3 by 0.2–0.6 mm, pubescent; pistillate ones terminal or axillary, racemes, axis up to 1.5 cm long, 0.6–1.1 mm diam, pubescent, bracts lanceolate, 0.6–2.5 by 0.3–0.8 mm, pubescent outside. Staminate flowers at least 3.5 mm diam; pedicel c. 1.2 mm long, c. 0.35 mm diam, pubescent; sepals elliptic, 1–1.7 by 0.3–0.8 mm, base connate, margin entire, apex acute, pubescent or hirsute outside; petals obovate, 3.4–4.5 by 1.4–2.5 mm, dark red-purple, glabrous; disc lobes rectangular, 0.35–0.5 by 0.35–0.45 mm, apex truncate to slightly rounded; stamens 5, anthers ellipsoid, 0.8–1 mm long, apically divaricate. Pistillate flowers (fruiting) 6–10.5 mm diam; pedicel thickening toward apex, 3.6–4.5 mm long, apically 1.5–2 mm diam, pubescent; sepals triangular to lanceolate, 8.5–10 by 3.5–4.6 mm, outer surface pubescent, sometimes marbled, mixed patches in dark red and yellow, inner surface glabrous, dark purplish red when dry, base connate, margin distantly serrate, teeth glandular, apex acuminate, ending in a gland; petals fallen, not seen; disc lobes semi-orbicular, 0.7–0.9 by 0.45–0.6 mm, apex rounded; ovary c. 1.5 mm diam, densely pubescent; style c. 0.2 mm long; stigmas apically deeply bifid, free arms 0.5–0.6 mm long. Fruits c. 1 cm diam, green; sepals persistent, green. Seeds not seen.

    Thailand.— PENINSULAR. Trang (Khao Soi Dao), Phatthalung.

    Distribution.— Endemic in Thailand.

    ▲= T. lanceoatus; «= T. pachyphyllus

    Ecology.— Evergreen forests, understorey, near streams. Flowering: March to April; fruiting: April.

    Notes.— 1. Section Trigonostemon.

    2. A rare species endemic to Thailand. It resembles T. capillipes in the 5 stamens and relatively large pistillate sepals, and was treated as a synonym in our previous revision (Yu & Van Welzen, Blumea 62, 2018: 191). However, after examining more collections, we reinstate the species here. The main spotting characters of T. pachyphyllus includes the coriaceous leaves (thick leaves as indicated by the specific epithet) and the discolorous surfaces when dry. In addition, the pistillate sepals sometimes display a marbled pattern on the outer surface and the inflorescences are considerably smaller.

12. Trigonostemon philippinensis Stapf, Leafl. Philipp. Bot. 1: 206. 1907 (‘philippinense’); Pax & K.Hoffm. in Engl., Pflanzenfam. IV.147.iii: 91. 1911; Merr., Enum. Philipp. Fl. Pl. 2: 452. 1923; Airy Shaw, Kew Bull. 36: 355. 1981; Alphab. Enum. Euphorb. Philipp. Isl.: 47. 1983; R.I.Milne, Kew Bull. 50: 27, in key, 29, in key. 1995; R.Y.Yu et al., Taxon 68: 930. 2019; R.Y.Yu & Welzen, Blumea 62 (2018) 206, fig. 11, map 9. — Trigonostemon thrysoideus Stapf, Bull. Misc. Inform., Kew 1909: 264. 1909 (‘thyrsoideum’); P.H.HÔ, Câyco Viêtnam 2(1): 344. 1992; Chantar., Thai Forest Bull. (Bot.) 33: 29. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 584, Plate XXXII: 1. 2007; P.T.Li & M.G.Gilbert. in C.Y.Wu, P.H.Raven & D.Y.Hong, Fl. China 11: 274. 2008. — Trigonostemon laoticus Gagnep., Bull. Soc. Bot. France 69: 751. 1922. — Prosartema stellaris Gagnep., Bull. Soc. Bot. France 71: 875. 1924. — Prosartema laotica Gagnep. in Lecomte, Fl. Indo-Chine 5: 306. 1925. — Trigonostemon stellaris (Gagnep.) Airy Shaw, Kew Bull. 32: 415. 1978. — Trigonostemon nigrifolius N.P.Balakr. & Chakrab., J. Econ. Taxon. Bot. 5: 173. 1984.

Trees or treelets, 6–15(–20) m tall, dbh 6–25(–40) cm, flowering branches up to 6.5 mm thick, brownish, glabrescent, slightly scaberulous basally. Outer bark hard, 0.5–1 mm thick, brownish to greyish, rugose, lenticellate; inner bark 2–5 mm thick, pinkish to reddish, brownish (when dry); exudate clear, pinkish; wood dirty pinkish white. Stipules falcate, sometimes linear, up to 1.5–2 by c. 0.4 mm, pubescent near base, caducous. Leaves: petiole terete, 1.5–15 cm long, 0.8–2.5 mm diam, glabrous or slightly pubescent, base in apical leaves often somewhat sheathing; blade elliptic to sometimes obovate, 10–31 by 4–13.5 cm, coriaceous, base acute or cuneate, with 2 adaxial falcate glands, margin distantly serrate to crenate, teeth subulate or falcate, apex acuminate to caudate, sometimes acute, dark green above, pale green beneath, both sides glabrous or with a few very scattered hairs; venation often slightly pubescent, midrib slightly raised above and raised beneath, nerves 8–14 pairs, curved, branched and connected along margin, veins and veinlets reticulate, obscure. Inflorescences often terminal, paniculate, much branched and many-flowered, up to 30 cm long (up to 15 cm long in the Philippines), usually unisexual to bisexual, finely pubescent; bracteate under each node, bracts triangular, 0.5–2.5(–5) by 0.2–1 mm (larger ones basal in inflorescence, smaller ones higher up; often longer in Thai and Vietnamese specimens), outside pubescent, inside glabrous, on large branches sometimes caducous and often with 2 falcate or subulate bracteoles at the sides (Sumatra and Borneo), up to 1 mm long. Staminate flowers c. 5 mm diam; pedicel 3.5–4 mm long, c. 0.2 mm thick, pubescent, articulate at base; sepals elliptic or somewhat obovate, 1.2–1.6 by 0.6–0.8 mm, pale greenish or greenish yellow, base narrowed and connate, margin somewhat translucent, apex rounded or slightly undulate, outside pubescent, often with a gland in the middle, inside glabrous; petals obovate to spathulate, 2.5–4 by 1.2–2 mm, base cuneate to claw-like, entire, apex rounded, yellowish, sometime pale cream inside and with a paler margin (Philippines), midrib and few parallel veins visible, glabrous; disc lobes trapezoid, 0.2–0.3 by 0.2–0.3 mm, c. 0.1 mm thick, fleshy, apex thickened, reflexed; stamens 3, androphore c. 0.5 mm long, free terminal part sometimes slightly trifid at top, sometimes bent (Sumatra and Borneo), anthers splitting off subapically from androphore, ellipsoid, c. 0.2 mm long, cream, divaricate (mainly in specimens from Thailand and Vietnam), connectives apically with droplets with secretion. Pistillate flowers of same size as staminate ones; pedicel 2.5–3.5 mm long, apex slightly thickened, 0.6–0.7 mm thick; sepals and petals as in staminate flowers; disc lobes rectangular, c. 0.4 by 0.6 mm, apex truncate; ovary c. 1 mm diam, glabrous and warty, styles extremely short, stigmas with a shallow groove above. Infructescence pendulous, dull pale light green. Fruits c. 1.5 cm diam, greenish, glabrous, warty or aculeate above; pedicel 2.5–4 cm long, green; sepals persistent but not accrescent; wall woody, c. 0.6 mm thick, exocarp partly detaching; columella c. 0.8 cm long. Seeds 6–7.5 mm diam, dark brown when dry; hilum long-triangular to heart-shaped, 1–2.5 by 0.5–1.2 mm.

    Thailand.— NORTHERN: Mae Hong Son, Chiang Mai (Doi Chiangdao, Doi Inthanon), Chiang Rai (Khunkorn waterfall), Nan (Ban Pa Gum, Doi Phu Kha National Park), Phrae (between Pha Tuem and Ban Phra).

    Distribution.— Myanmar, China (Yunnan: type), Thailand, Laos, Vietnam, Malay Peninsula, Sumatra, Borneo, Philippines.

    Ecology.— Lowland evergreen to deciduous forests, sometimes on limestone hills, near rivers; growing on red to yellow calcareous soils to granite bedrocks. Altitude: 600-1,500 m. Flowering and fruiting: all year round.

    Note.— Section Tylosepalum.

13. Trigonostemon quocensis Gagnep., Bull. Soc. Bot. France 69: 753. 1923; in Lecomte, Fl. Indo-Chine 5: 316. 1925; Airy Shaw, Kew Bull. 26: 348. 1972. P.H.HÔ, Câyco Viêtnam 2(1): 343. 1992; Chantar., Thai Forest Bull. (Bot.) 33: 27. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 582. 2007; R.Y.Yu et al., Taxon 68: 930. 2019; R.Y.Yu & Welzen, Blumea 65: 41, map 6. 2020. — Trigonostemon birmanicus Chakrab. & N.P.Balakr., J. Econ. Taxon. Bot. 5: 175. 1984.

Shrubs or small trees, 0.5–5 m tall, dhb 6–8 cm; flowering branches 1–3.8 mm diam, pubescent when young, glabrous in old parts. Indumentum of simple hairs; translucent (oil?) dots sometimes present in green parts. Outer bark 0.1–0.2 mm thick, dark brown; inner bark 0.1–0.2 mm thick, reddish brown, solidified sap reddish black; wood yellow. Stipules subulate, 0.2–0.7 mm long, caducous, sometimes pubescent at base. Leaves: petiole terete, (0.6–)1–6.1 cm long, 0.8–2 mm diam, glabrous or pubescent, sometimes thickened at apex and base; blade ovate to elliptic, 8–24 by 3.6–10 cm, chartaceous, base truncate, rounded, acute or sometimes cordate, 2 adaxial glands present, sometimes pubescent, margin distantly serrate, apex acuminate to caudate, both surfaces pubescent when young, glabrous when mature; venation triplinerved (basal secondary veins often as thick as other secondary veins), midrib and sometimes secondary veins flat or slightly raised above and distinctively elevated and pubescent beneath, other secondary veins 6–9 pairs, bow-shaped and connected along margin, tertiary veins scalariform, veinlets reticulate. Inflorescences bisexual, terminal or axillary, large panicles, pistillate flowers open before staminate ones; main axis terete, up to 44 cm long, 0.6–1.5 mm diam, pubescent; bracts linear to lanceolate, 1–12 by 0.15–1(–2.1) mm, often pubescent. Staminate flowers 4.4–5.5 mm diam, buds usually globose; pedicel 3.5–7.5 mm long, 0.15–0.3 mm diam, glabrous; sepals ovate to elliptic, 1.4–2.5 by 0.8–2.2 mm, base connate, margin entire, apex acute to rounded, pubescent outside; petals obovate to flabellate, 2.1–3.9 by 1.7–2.5 mm, contort, yellow, lower part sometimes claw-like, apex rounded, glabrous; disc annular, fleshy, margin entire, 0.4 (inner margin)–0.8 mm (outer margin) diam; stamens 3, androphore 0.3–0.6 mm long, 0.2–0.3 mm diam, free part of filaments 0.4–0.5 mm long, anthers free, globose to ellipsoid, 0.4–0.5 mm long. Pistillate flowers 6–7 mm diam, buds somewhat conical; pedicel thickening toward apex, 2–5.5 mm long, apically 0.5–0.9 mm diam when flowering, elongating to 4–9 mm long, apically 0.6–1 mm diam when fruiting, pubescent; sepals lanceolate to elliptic, 1.5–4.5 by 0.7–1.6 mm, base connate, margin entire, apex acute to acuminate; petals and disc as staminate flowers; ovary 1–1.2 mm diam, densely pubescent, style indistinct, stigmas 0.4–1 mm long, slightly thickened and sometimes slightly bifid at apex. Fruits 1–1.1 cm diam, hirsute; sepals persistent, but not accrescent; wall 0.3–0.4(–0.5) mm thick, exocarp not detaching; columella 4.5–6.5 mm long. Seeds 6–7 mm diam, marbled; hilum orbicular or rhombic, 1.2–1.7 by 1.1–1.5 mm.

    Thailand.— EASTERN: Nakhon Ratchasima (Katok, Pak Thongchai, Sikhiu); SOUTH-WESTERN: Prachuap Khiri Khan; SOUTH-EASTERN: Chanthaburi (Khao Soi Dao Nua); PENINSULAR: Ranong (Khao Pawta Chong Dong), Surat Thani (Khao Wong, Khiriratnikom), Phangnga (Khao Nang Hong, Trap Put), Nakhon Si Thammarat, Phatthalung (Klong Hui Kao).

    Distribution.— Myanmar (Upper Chindwin, in Sagaing or Kachin region), Thailand, Indo-China (Cambodia type).

    « = T. eberhardtii; X = T. quocensis

    Ecology.— Understorey in dry evergreen forests, on limestone. Elevation: 50–820 m. Flowering: all year round; fruiting: March, September.

    Notes.— 1. Section Tylosepalum.

 2. The species is relatively common in Thailand and Vietnam. The plant sometimes has the similar translucent (oil?) dots in the green parts as T. eberhardtii. The staminate buds are usually globose (petals still contort), but in most other species they are often conical.

14. Trigonostemon reidioides (Kurz) Craib, Bull. Misc. Inform., Kew 1911: 464. 1911; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vi: 128. 1912; Gagnep. in Lecomte, Fl. Indo-Chine 5: 316. 1925; P.H.HÔ, Câyco Viêtnam 2(1): 343. 1992; Chantar., Thai Forest Bull. (Bot.) 33: 28. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 582, Fig. 95, Plate XXX: 3. 2007; R.Y.Yu et al., Taxon 68: 929. 2019; R.Y.Yu & Welzen, Blumea 65: 42, map 13. 2020. — Baliospermum reidioides Kurz, Flora 58: 32. 1875; For. Fl. Brit. Burma 2: 411. 1877; Hook.f., Fl. Brit. Ind. 5: 461. 1887; Williams, Bull. Herb. Boiss. Ser. 2,5: 32. 1905; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vi: 29. 1912. — Trigonostemon hybridus Gagnep., Bull. Soc. Bot. France 69: 750. 1922. — Trigonostemon rubescens Gagnep., Bull. Soc. Bot. France 69: 754. 1922.

Shrubs, 0.5–1.5 m tall; flowering branches 1.2–3.2 mm diam, slightly to densely pubescent. Indumentum of simple and stellately bundled hairs. Outer bark c. 0.1 mm thick, greyish to dark brown; inner bark 0.1–0.2 mm thick, dark reddish, sap clear, watery, black or dark red in dry material; wood yellow or brown. Stipules acicular to subulate, 0.6–2.3 mm long, caducous, pubescent at base. Leaves: petiole terete, slightly grooved above, 0.5–2.5 cm long, 0.6–1.9 mm diam, densely pubescent to glabrescent; blade oblong to elliptic, rarely obovate or (ob)lanceolate, 3.5–15 by 0.5–6.3 cm, chartaceous to coriaceous, base acute to rounded, adaxial glands 2, falcate, blackish, margin entire, apex acute to acuminate, upper surface dull dark green, lower surface dull light green, both surfaces densely to slightly pubescent, when slightly pubescent then often only simple hairs present; venation triplinerved, pubescent on both sides, midrib and basal secondary veins flat above and elevated below, other secondary veins 2–8 pairs, bow-shaped and connected along margin, tertiary veins and veinlets reticulate. Inflorescences bisexual, axillary or terminal large panicles; main axis terete, 3–29 cm long, 0.4–1.2 mm diam, dull red, often pubescent, rarely glabrescent; bracts lanceolate to linear, 0.5–17 by 0.1–1.9 mm, pubescent. Staminate flowers 4.1–6.6 mm diam; pedicel 2.5–7 mm long, 0.15–0.5 mm diam, pale light green to dull reddish, pubescent to glabrescent; sepals elliptic, 1–2.6 by 0.5–1.6 mm, pale light green to dull light yellow or reddish, base connate, margin entire, sometimes ciliate, apex acute to rounded, pubescent to glabrescent outside; petals obovate to spathulate, 3.3–6.4 by 1.6–4.2 mm, white, dark red, deep maroon or dark purple, lower part sometimes clawlike, apex rounded, glabrous; disc annular, somewhat plicate, light orange, glabrous, margin undulate, 0.3–0.45 mm wide; stamens 3, androphore 0.35–0.7 mm long, 0.2–0.5 mm diam, cream, anthers ellipsoid, 0.5–0.8 mm long, cream. Pistillate flowers 5.3 – 8.9(–13) mm diam; pedicel slightly thickening toward apex, 8–20 mm long, apically 0.4–1 mm diam when flowering, elongating in fruit to (0.8–)1.6–3.4 cm long, apically 0.7–1.5 mm diam, pubescent, glabrescent; sepals elliptic to oblong, 3–6 by 1.1–2.2 mm, base connate, margin entire, sometimes ciliate, apex acute to acuminate, pubescent outside; petals as staminate flowers but larger, 5.9–9 by 2.6–6 mm; disc as staminate flowers; ovary 1.3–1.6 mm diam, pubescent, light yellow or green, style absent, stigmas thickening toward apex, 0.7–0.8 mm long, apically 0.5–0.6 mm wide, white, pale light yellow or cream, furrowed above, apically not bifid. Fruits 1–1.3 cm diam, green, pubescent; sepals persistent but not accrescent; wall 0.4–0.6 mm thick, exocarp partly detaching; columella 4.2–5.8 mm long. Seeds 4.6–6.3 mm diam, often marbled; hilum oblong to elliptic to triangular, 0.7–1.8 by 0.5–1 mm.

    Thailand.— NORTHERN: Tak (Ban Na, Doi Muser), Sukhothai (Khao Luang), Phitsanulok (Thung Salang Luang); NORTH-EASTERN: Phetchabun, Loei (Wang Sapung), Udon Thani, Nong Khai (Bung Khla, Dong Srichompoo, Phon Phisai, Seka), Sakon Nakhon (Phu Phan, Wa Nawn), Nakhon Phanom (Phu Langka), Kalasin, Maha Sarakham (Ban Ta Yae, Kosumpisai), Khon Kaen (Tha Phra); EASTERN: Chaiyaphum, Nakhon Ratchasima (Bua Yai, Khao Yai), Buri Rum (Nang Rong), Surin (Sangka), Si Sa Ket (Kantharom), Ubon Ratchathani (Phu Jong Nayoy National Park); SOUTH-WESTERN: Uthai Thani (Huay Ka Kang), Kanchanaburi (Khao Thong, Wang Kanai, TEYSMANN 5981, isotype K), Phetchaburi (Cha-am), Ratchaburi, Prachuap Khiri Khan (Nong Kae); SOUTH-EASTERN: Sa Kaeo (Aranya Prathet), Prachin Buri, Chon Buri (Sriracha), Rayong (Ban Chak Done), Chanthaburi (Makham), Trat (Klong Yai, Takam).

    Distribution.— Thailand, Laos, Cambodia, Vietnam.

    Ecology.— Often in open areas in dry dipterocarp forests, or in seasonal deciduous pine or Melaleuca forests, occasionally in waste lands or swampy forests. Often growing in sandy or rocky soil, sometimes along roads or rivers. Elevation: 20–1100 m. Flowering: all year round; fruiting: January to June, August, October.

    Vernacular.- Khaao yen noen (ข้าวเย็นเนิน) (Ratchaburi, Prachuap Khiri Khan); Duu bia (ดู่เบี้ย), Duu tia (ดู่เตี้ย) (Phetchaburi); Thanong, Rak thanong (รักทะนง) (Nakhon Ratchasima); Tha nong daeng (ทะนงแดง) (Prachuap Khiri Khan); Naanng saeng (นางแซง) (Ubon Ratchathani); Lot thanong (โลดทะนง) (Ratchaburi, Prachin Buri, Trat); Lot thanong daeng (โลดทะนงแดง) (Buriram); Naat kham (หนาดคำ) (Northern); Hua yaa khaao yen noen (หัวยาข้าวเย็นเนิน) (Ratchaburi).

    Uses.— Roots applied for emetic, anti-asthmatic medicine and as laxative.

     Notes.— 1. Section Spinipollen.

2. This is a common species in Thailand and Indochina. The species displays a continuous variation in the indumentum: from very dense stellately bundled hairs (as represented by the type collection of T. reidioides) to relatively sparse and mostly simple hairs (but stellately bundled hairs are still present; as in the type collections of T. rubescens). Trigonostemon hybridus represents an intermediate form between the above mentioned two, and Gagnepain (1922) even considered it as a hybrid form. As morphological discontinuities are lacking, T. hybridus and T. rubescens are placed in synonymy. Only two species of Trigonostemon (the other species is T. balgooyi R.Y.Yu & Welzen from Johor, Malaysia) have an indumentum of both simple and stellately bundled hairs, making it a useful character in identification. 

15. Trigonostemon verticillatus (Jack) Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii: 87. 1910; Jablonski, Brittonia 15: 164. 1963; Chantar., Thai Forest Bull. (Bot.) 33: 30. 2005; in Welzen & Chayam., Fl. Thailand 8, 2: 585, Plate XXXI: 2. 2007; R.Y.Yu & Welzen, Blumea 62: 213, map 11. 2018; R.Y.Yu et al., Taxon 68: 928. 2019; R.Y.Yu & Welzen, Blumea 65: 44, map 14. 2020. — Enchidium verticillatum Jack, Malayan Misc. 2: 90. 1822; Comp. Bot. Mag. 1: 257. 1836 (excl. syn. Rumph.); Müll. Arg. in DC., Prodr. 15, 2: 1256. 1866; Merr., J. Arnold Arb. 33: 224. 1952. — Telogyne indica Baill., Étude Gén. Euphorb.: 238. 1858. — Trigonostemon indicus (Baill.) Müll.Arg., Linnaea 34: 214. 1865; in DC., Prodr. 15, 2: 1107. 1866; Hook.f., Fl. Brit. Ind. 5: 398. 1887; Ridl., Fl. Malay Penins. 3: 264. 1924.

Small trees, up to 8 m tall; flowering branches terete, 2.5–3 mm diam. Bark 0.4–0.5 mm thick, pale greyish; wood pale yellowish. Stipules subulate, 0.5–1.5 mm long, blackish and pubescent near base, yellowish at apex. Leaves: petiole wrinkled, terete but grooved above, 2–9 cm long, often thickened at apex and base; blade oblong, elliptic or lanceolate, occasionally linear, 10–22 by (1.5–)2.5–5 cm, chartaceous or coriaceous, base acute to rounded, 1 or 2 pairs of glands adaxially present, subulate or falcate, often glabrous, margin distantly serrate, teeth subulate, apex acuminate to caudate, upper surface dark green, lower surface pale green, both sides glabrous; midrib slightly raised above and distinctly elevated beneath, nerves 12–21 pairs, connected along margin, veinlets reticulate, often obscure. Inflorescences bisexual, terminal or subterminal, racemes (spike-like) or thyrses, often puberulent, main rachis up to 10 cm long, involucral bracts triangular to lanceolate to falcate, 1–2 by c. 0.5 mm, with 2 lateral bracteoles; bracts to flowers broadly triangular, somewhat sheathing, up to 1 by 1 mm, apex acuminate, puberulent. Staminate flowers c. 4 mm diam (unopened); pedicel slightly thickened towards apex, 1.5–3 mm long, apically 0.6–0.8 mm diam, glabrous or very slightly puberulent; sepals often unequal, orbicular to ovate, 1–1.5 by 1–1.5 mm, imbricate, apex rounded, outside glabrous or slightly puberulent, margin ciliate; petals ovate, 2.5–2.8 by c. 2 mm, dark reddish, contort, apex rounded, outer surface glabrous, inner surface rough and slightly papillose, margin entire, occasionally slightly ciliate; disc annular when young and cupular when mature, c. 0.5 mm wide, margin often with 5 notches; stamens 5, androphore c. 0.5 mm long, anthers ellipsoid, c. 1 mm long, divaricate, connectives apically with numerous droplets (or expanded cells) with secretion. Pistillate flowers c. 5 mm diam; pedicel as staminate flowers but longer and thicker, c. 4 mm long, c. 1 mm diam; sepals elliptic, c. 1.5 by 1 mm when flowering, more or less accrescent to 3 by 2 mm when fruiting, apex rounded, outside slightly puberulent, margin ciliate; petals as staminate flowers, caducous; disc annular, subentire; ovary 1.2–1.5 mm diam, puberulent, style c. 0.2 mm long, sometimes indistinct, stigmas c. 0.7 mm long, bifid at apex, arms c. 0.5 mm long, thickened abaxially, reniform at base. Fruits c. 1 cm diam, outside finely puberulent; wall 0.7–1 mm thick, exocarp detaching. Seeds c. 5.5 mm diam; hilum rhombic, c. 1.8 by 1 mm.

    Thailand.— SOUTH-EASTERN: Chanthaburi (Phliu waterfall, Khao Sabap); PENINSULAR: Ranong (Kam Puam, Klong Naka), Phangnga (Ko Yao Yai, Takuapa), Narathiwat (Sukhirin).

    Distribution.— T. verticillatus var. verticillatus is the only variety in Thailand, also in Malaysia (neotype). Trigonostemon verticillatus var. salicifolius (Ridl.) Whitmore is endemic in the Malay Peninsula.

    Ecology.— Primary dipterocarp and evergreen forests on hillsides or near the sea, growing in peat swamps. Altitude: 60–400 m. Flowering: December to April.

    Note.— Section Trigonostemon.

16. Trigonostemon viridissimus (Kurz) Airy Shaw, Kew Bull. 25: 545. 1971; Whitmore, Tree Fl. Malaya 2: 135. 1973; Airy Shaw, Kew Bull., Addit. Ser. 5: 205. 1975; Kew Bull. 36: 358. 1981; Kew Bull. 37: 36. 1982; R.I.Milne, Kew Bull. 50: 28, in key, 29, in key. 1955; R.Y.Yu & Welzen, Blumea 62: 221, map 14. 2018; R.Y.Yu et al., Taxon 68: 930. 2019; R.Y.Yu & Welzen, Blumea 65: 44, map 15. 2020. — Sabia viridissima Kurz, J. Asiac. Soc. Bengal part 2, 41: 304. 1872. — Blachia viridissima (Kurz) King, J. Asiac. Soc. Bengal 65: 455, in obs. 1896. — Trigonostemon ovatifolius J.J.Sm., Meded. Dep. Landb. 10: 583. 1910. — Trigonostemon membranaceus Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii: 91. 1911. — Trigonostemon sumatranus Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii: 90. 1911. — Trigonostemon macgregorii Merr., Philipp. J. Sci. 16: 566. 1920. — Neotrigonostemon diversifolius Pax & K.Hoffm., Notizbl. Königl. Bot. Gart. Berlin 10: 385. 1928. — Trigonostemon chatterjii Deb & G.K.Deka, Indian Forester 91: 577. 1965. — Kurziodendron viridissimum (Kurz) N.P.Balakr., Bull. Bot. Surv. India 8: 68, pl. 1, fig. 1–7. 1966. — Trigonostemon viridissimus (Kurz) Airy Shaw var. chatterjii (Deb & G.K.Deka) N.P.Balakr. & Chakrab., J. Econ. Taxon. Bot. 5: 967. 1984. — Trigonostemon viridissimus (Kurz) Airy Shaw var. confertifolius N.P.Balakr. & N.G.Nair, Bull. Bot. Surv. India 24: 36. 1982. — Trigonostemon huangmosu Y.T.Chang, Guihaia 3: 174. 1983.

Shrubs or small trees, 1–10 m tall, stem up to 10 cm diam; flowering branches 1.5–3.2(–4.6) mm diam, pubescent when young, glabrescent. Indumentum of simple hairs; translucent (oil?) dots often present in green parts. Bark 0.1–0.3 mm thick, grey or pale to reddish brown or grey; wood pale yellowish, pith sometimes hollow. Stipules subulate to nipple-like, 0.4–1.5 mm long, caducous, often pubescent at base. Leaves: petiole terete but grooved above, 0.5–3.5(–5.5) cm long, 0.7–1.8 mm diam, wrinkled, pubescent when young; blade ovate to elliptic to oblong, sometimes (ob)ovate, (4.5–)8–24 by (1.5–)2.5–9 cm, membranous to chartaceous, base acute or obtuse, often with 1–2 pairs of adaxial glands, margin entire or slightly distantly serrate, apex acuminate to caudate, upper surface glabrescent to glabrous, dark green, lower surface often sparsely pubescent, paler and dull green; venation triplinerved, midrib slightly raised above and elevated beneath, often pubescent, especially near base, secondary veins 5–10 pairs, bow-shaped and connected along margin, tertiary veins scalariform, veinlets reticulate. Inflorescences bisexual, terminal or axillary, loose panicles; main axis terete, up to 30 cm long, 0.4–2 mm diam, slightly pubescent; bracts lanceolate, 0.5–6 by 0.2–1 mm, pubescent. Staminate flowers 5–9 mm diam; buds conical; pedicel 4.5–9 mm long, 0.15–0.2 mm diam, glabrescent or slightly pubescent; sepals elliptic to orbicular to triangular, 1–1.7 by 0.6–1.2 mm, imbricate, margin somewhat undulate, apex rounded or truncate, sometimes with a short notch and an apical gland, pubescent outside; petals obovate, 3–6.5(–10) by 2.5–4.5(–7) mm, contort, membranous, with several distinct parallel veins, base cuneate or somewhat claw-like, entire, apex rounded, yellow to orange, glabrous; disc annular, margin undulate, reflexed, sometimes with 5 notches; stamens 3, androphore 0.7–1.5 mm long, free part of filaments 0.3–0.4(–0.6) mm long, anthers free, ellipsoid, 0.4–0.5 mm long. Pistillate flowers 5–9 mm diam; buds conical; pedicel slightly thickening toward apex, 0.3–1.4 cm long, apically 0.5–0.7 mm diam when flowering, elongating up to 1.1–2.9 cm long and 0.8–2 mm diam in fruit, glabrescent, often with translucent (oil?) dots; sepals, petals and disc as staminate flowers, petals caducous when fruiting; ovary 0.8–1.1 mm diam, glabrous, with numerous translucent (oil?) dots on surface, styles 0.2–0.7 mm long, stigmas 0.5–1.5 mm long, erect or bent, apically slightly thickened and slightly bifid or horseshoe-like. Fruits 1.1–1.5 cm diam, greenish, glabrous, smooth; sepals persistent but not accrescent; wall 0.4–0.5 mm thick, exocarp partly detaching; columella 5–6.3 mm long. Seeds 7–8 mm diam, with numerous translucent (oil?) dots on surface; hilum rhombic to oblong, 1.5 by 0.6–1.2 mm.

    Distribution. — India, Myanmar (Mergui), China, Laos, Thailand, Vietnam, Malay Peninsula, Sumatra, Java, Borneo, Philippines, Lesser Sunda Islands.

    Ecology.— Primary to secondary forests, along coasts to hillsides, sometimes along rivers.

    Notes.— 1. Section Tylosepalum.

2. The species has perhaps the widest distribution in the genus and displays a wide range of morphological variation, even within its type locality, the Andamans (India). The variation appears to be continuous.

3. In Thailand only var. viridissimus is found, which differs in the pendulous and hairy inflorescences, style up to 0.7 mm long and stigmas often erect, from var. elegantissimus that has erect and glabrous inflorescences, style to 0.4 mm long and stigmas bent (and occurs in China, Laos, Vietnam, Malay Peninsula, Borneo).